In a pressure sensor described in U.S. Pat. No. 6,651,508 (corresponding to JP-A-2002-221462), a pressure detection element is located in a casing, and the casing is filled with a gel material so as to seal the pressure detection element. The gel material is exposed from an opening portion of the casing so that the pressure of a pressure medium is applied to the pressure detection element through the gel material.
In this pressure sensor, because the pressure detection element is sealed by the gel material, the pressure detection element can be protected from moisture or foreign material contained in the pressure medium. However, when the pressure sensor is used in an exhaust gas environment having a high humidity or a high acidity, for example, the moisture contained in the pressure medium adheres on the casing and the gel material exposed from the opening portion of the casing, and stays thereon as condensed water. In this case, if the condensed water is frozen, an extra force is applied to the gel material, and the pressure transmission of the gel material is deteriorated. Furthermore, when water having a high corrosion property stays on the gel material, the gel material is deteriorated, and the pressure sensor cannot accurately detect the pressure of the pressure medium.